--- wikisrc/guide/pam.mdwn 2013/03/10 02:18:51 1.2
+++ wikisrc/guide/pam.mdwn 2013/03/10 09:58:15 1.3
@@ -2,103 +2,106 @@
## About
-This article describes the underlying principles and mechanisms of the
-*Pluggable Authentication Modules (PAM)* library, and explains how to configure
+This article describes the underlying principles and mechanisms of the
+*Pluggable Authentication Modules (PAM)* library, and explains how to configure
PAM, how to integrate PAM into applications, and how to write PAM modules.
See on the bottom of the page for the license of this text.
## Introduction
-The Pluggable Authentication Modules (PAM) library is a generalized API for
-authentication-related services which allows a system administrator to add new
-authentication methods simply by installing new PAM modules, and to modify
+The Pluggable Authentication Modules (PAM) library is a generalized API for
+authentication-related services which allows a system administrator to add new
+authentication methods simply by installing new PAM modules, and to modify
authentication policies by editing configuration files.
-PAM was defined and developed in 1995 by Vipin Samar and Charlie Lai of Sun
-Microsystems, and has not changed much since. In 1997, the Open Group published
-the X/Open Single Sign-on (XSSO) preliminary specification, which standardized
-the PAM API and added extensions for single (or rather integrated) sign-on. At
-the time of this writing, this specification has not yet been adopted as a
+PAM was defined and developed in 1995 by Vipin Samar and Charlie Lai of Sun
+Microsystems, and has not changed much since. In 1997, the Open Group published
+the X/Open Single Sign-on (XSSO) preliminary specification, which standardized
+the PAM API and added extensions for single (or rather integrated) sign-on. At
+the time of this writing, this specification has not yet been adopted as a
standard.
-Although this article focuses primarily on FreeBSD 5.x and NetBSD 3.x, which
-both use OpenPAM, it should be equally applicable to FreeBSD 4.x, which uses
+Although this article focuses primarily on FreeBSD 5.x and NetBSD 3.x, which
+both use OpenPAM, it should be equally applicable to FreeBSD 4.x, which uses
Linux-PAM, and other operating systems such as Linux and Solaris.
## Terms and conventions
### Definitions
-The terminology surrounding PAM is rather confused. Neither Samar and Lai's
-original paper nor the XSSO specification made any attempt at formally defining
-terms for the various actors and entities involved in PAM, and the terms that
-they do use (but do not define) are sometimes misleading and ambiguous. The
-first attempt at establishing a consistent and unambiguous terminology was a
-whitepaper written by Andrew G. Morgan (author of Linux-PAM) in 1999. While
-Morgan's choice of terminology was a huge leap forward, it is in this author's
-opinion by no means perfect. What follows is an attempt, heavily inspired by
-Morgan, to define precise and unambiguous terms for all actors and entities
+The terminology surrounding PAM is rather confused. Neither Samar and Lai's
+original paper nor the XSSO specification made any attempt at formally defining
+terms for the various actors and entities involved in PAM, and the terms that
+they do use (but do not define) are sometimes misleading and ambiguous. The
+first attempt at establishing a consistent and unambiguous terminology was a
+whitepaper written by Andrew G. Morgan (author of Linux-PAM) in 1999. While
+Morgan's choice of terminology was a huge leap forward, it is in this author's
+opinion by no means perfect. What follows is an attempt, heavily inspired by
+Morgan, to define precise and unambiguous terms for all actors and entities
involved in PAM.
- * *account* -- The set of credentials the applicant is requesting from the
+ * *account* -- The set of credentials the applicant is requesting from the
arbitrator.
* *applicant* -- The user or entity requesting authentication.
- * *arbitrator* -- The user or entity who has the privileges necessary to verify
+ * *arbitrator* -- The user or entity who has the privileges necessary to verify
the applicant's credentials and the authority to grant or deny the request.
- * *chain* -- A sequence of modules that will be invoked in response to a PAM
- request. The chain includes information about the order in which to invoke
- the modules, what arguments to pass to them, and how to interpret the
+ * *chain* -- A sequence of modules that will be invoked in response to a PAM
+ request. The chain includes information about the order in which to invoke
+ the modules, what arguments to pass to them, and how to interpret the
results.
- * *client* -- The application responsible for initiating an authentication
- request on behalf of the applicant and for obtaining the necessary
+ * *client* -- The application responsible for initiating an authentication
+ request on behalf of the applicant and for obtaining the necessary
authentication information from him.
- * *facility* -- One of the four basic groups of functionality provided by PAM:
- authentication, account management, session management and authentication
+ * *facility* -- One of the four basic groups of functionality provided by PAM:
+ authentication, account management, session management and authentication
token update.
- * *module* -- A collection of one or more related functions implementing a
- particular authentication facility, gathered into a single (normally
+ * *module* -- A collection of one or more related functions implementing a
+ particular authentication facility, gathered into a single (normally
dynamically loadable) binary file and identified by a single name.
- * *policy* -- The complete set of configuration statements describing how to
- handle PAM requests for a particular service. A policy normally consists of
- four chains, one for each facility, though some services do not use all four
+ * *policy* -- The complete set of configuration statements describing how to
+ handle PAM requests for a particular service. A policy normally consists of
+ four chains, one for each facility, though some services do not use all four
facilities.
- * *server* -- The application acting on behalf of the arbitrator to converse
- with the client, retrieve authentication information, verify the applicant's
+ * *server* -- The application acting on behalf of the arbitrator to converse
+ with the client, retrieve authentication information, verify the applicant's
credentials and grant or deny requests.
- * *service* -- A class of servers providing similar or related functionality
- and requiring similar authentication. PAM policies are defined on a
- per-service basis, so all servers that claim the same service name will be
+ * *service* -- A class of servers providing similar or related functionality
+ and requiring similar authentication. PAM policies are defined on a
+ per-service basis, so all servers that claim the same service name will be
subject to the same policy.
- * *session* -- The context within which service is rendered to the applicant by
- the server. One of PAM's four facilities, session management, is concerned
+ * *session* -- The context within which service is rendered to the applicant by
+ the server. One of PAM's four facilities, session management, is concerned
exclusively with setting up and tearing down this context.
- * *token* -- A chunk of information associated with the account, such as a
- password or passphrase, which the applicant must provide to prove his
+ * *token* -- A chunk of information associated with the account, such as a
+ password or passphrase, which the applicant must provide to prove his
identity.
- * *transaction* -- A sequence of requests from the same applicant to the same
- instance of the same server, beginning with authentication and session set-up
+ * *transaction* -- A sequence of requests from the same applicant to the same
+ instance of the same server, beginning with authentication and session set-up
and ending with session tear-down.
### Usage examples
-This section aims to illustrate the meanings of some of the terms defined above by way of a handful of simple examples.
+This section aims to illustrate the meanings of some of the terms defined above
+by way of a handful of simple examples.
#### Client and server are one
-This simple example shows `alice` [su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386)'ing to `root`.
+This simple example shows `alice`
+[su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386)'ing to
+`root`:
$ whoami
alice
@@ -111,15 +114,18 @@ This simple example shows `alice` [su(1)
* The applicant is `alice`.
* The account is `root`.
- * The [su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386) process is both client and server.
+ * The [su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386)
+ process is both client and server.
* The authentication token is `xi3kiune`.
- * The arbitrator is `root`, which is why [su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386) is setuid `root`.
+ * The arbitrator is `root`, which is why
+ [su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386) is
+ setuid `root`.
#### Client and server are separate
-The example below shows `eve` try to initiate an
-[ssh(1)](http://netbsd.gw.com/cgi-bin/man-cgi?ssh+1+NetBSD-5.0.1+i386)
-connection to `login.example.com`, ask to log in as `bob`, and succeed. Bob
+The example below shows `eve` try to initiate an
+[ssh(1)](http://netbsd.gw.com/cgi-bin/man-cgi?ssh+1+NetBSD-5.0.1+i386)
+connection to `login.example.com`, ask to log in as `bob`, and succeed. Bob
should have chosen a better password!
$ whoami
@@ -133,8 +139,12 @@ should have chosen a better password!
$
* The applicant is `eve`.
- * The client is Eve's [ssh(1)](http://netbsd.gw.com/cgi-bin/man-cgi?ssh+1+NetBSD-5.0.1+i386) process.
- * The server is the [sshd(8)](http://netbsd.gw.com/cgi-bin/man-cgi?sshd+8+NetBSD-5.0.1+i386) process on `login.example.com`
+ * The client is Eve's
+ [ssh(1)](http://netbsd.gw.com/cgi-bin/man-cgi?ssh+1+NetBSD-5.0.1+i386)
+ process.
+ * The server is the
+ [sshd(8)](http://netbsd.gw.com/cgi-bin/man-cgi?sshd+8+NetBSD-5.0.1+i386)
+ process on `login.example.com`
* The account is `bob`.
* The authentication token is `god`.
* Although this is not shown in this example, the arbitrator is `root`.
@@ -150,235 +160,238 @@ The following is FreeBSD's default polic
sshd session required pam_lastlog.so no_fail
sshd password required pam_permit.so
- * This policy applies to the `sshd` service (which is not necessarily
- restricted to the
- [sshd(8)](http://netbsd.gw.com/cgi-bin/man-cgi?sshd+8+NetBSD-5.0.1+i386)
+ * This policy applies to the `sshd` service (which is not necessarily
+ restricted to the
+ [sshd(8)](http://netbsd.gw.com/cgi-bin/man-cgi?sshd+8+NetBSD-5.0.1+i386)
server.)
* `auth`, `account`, `session` and `password` are facilities.
- * `pam_nologin.so`, `pam_unix.so`, `pam_login_access.so`, `pam_lastlog.so` and
- `pam_permit.so` are modules. It is clear from this example that `pam_unix.so`
+ * `pam_nologin.so`, `pam_unix.so`, `pam_login_access.so`, `pam_lastlog.so` and
+ `pam_permit.so` are modules. It is clear from this example that `pam_unix.so`
provides at least two facilities (authentication and account management.)
There are some differences between FreeBSD and NetBSD PAM policies:
* By default, every configuration is done under `/etc/pam.d`.
- * If configuration is non-existent, you will not have access to the system, in
+ * If configuration is non-existent, you will not have access to the system, in
contrast with FreeBSD that has a default policy of allowing authentication.
- * For authentication, NetBSD forces at least one `required`, `requisite` or
+ * For authentication, NetBSD forces at least one `required`, `requisite` or
`binding` module to be present.
## PAM Essentials
### Facilities and primitives
-The PAM API offers six different authentication primitives grouped in four
+The PAM API offers six different authentication primitives grouped in four
facilities, which are described below.
- * `auth` -- *Authentication.* This facility concerns itself with authenticating
- the applicant and establishing the account credentials. It provides two
+ * `auth` -- *Authentication.* This facility concerns itself with authenticating
+ the applicant and establishing the account credentials. It provides two
primitives:
- * [pam\_authenticate(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_authenticate+3+NetBSD-5.0.1+i386)
- authenticates the applicant, usually by requesting an authentication token
- and comparing it with a value stored in a database or obtained from an
+ * [pam\_authenticate(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_authenticate+3+NetBSD-5.0.1+i386)
+ authenticates the applicant, usually by requesting an authentication token
+ and comparing it with a value stored in a database or obtained from an
authentication server.
- * [pam\_setcred(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_setcred+3+NetBSD-5.0.1+i386)
- establishes account credentials such as user ID, group membership and
+ * [pam\_setcred(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_setcred+3+NetBSD-5.0.1+i386)
+ establishes account credentials such as user ID, group membership and
resource limits.
- * `account` -- *Account management.* This facility handles
- non-authentication-related issues of account availability, such as access
- restrictions based on the time of day or the server's work load. It provides
+ * `account` -- *Account management.* This facility handles
+ non-authentication-related issues of account availability, such as access
+ restrictions based on the time of day or the server's work load. It provides
a single primitive:
- * [pam\_acct\_mgmt(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_acct_mgmt+3+NetBSD-5.0.1+i386)
+ * [pam\_acct\_mgmt(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_acct_mgmt+3+NetBSD-5.0.1+i386)
verifies that the requested account is available.
- * `session` -- *Session management.* This facility handles tasks associated
- with session set-up and tear-down, such as login accounting. It provides two
+ * `session` -- *Session management.* This facility handles tasks associated
+ with session set-up and tear-down, such as login accounting. It provides two
primitives:
- * [pam\_open\_session(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_open_session+3+NetBSD-5.0.1+i386)
- performs tasks associated with session set-up: add an entry in the `utmp`
+ * [pam\_open\_session(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_open_session+3+NetBSD-5.0.1+i386)
+ performs tasks associated with session set-up: add an entry in the `utmp`
and `wtmp` databases, start an SSH agent, etc.
- * [pam\_close\_session(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_close_session+3+NetBSD-5.0.1+i386)
- performs tasks associated with session tear-down: add an entry in the
+ * [pam\_close\_session(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_close_session+3+NetBSD-5.0.1+i386)
+ performs tasks associated with session tear-down: add an entry in the
`utmp` and `wtmp` databases, stop the SSH agent, etc.
- * `password` -- *Password management.* This facility is used to change the
- authentication token associated with an account, either because it has
- expired or because the user wishes to change it. It provides a single
+ * `password` -- *Password management.* This facility is used to change the
+ authentication token associated with an account, either because it has
+ expired or because the user wishes to change it. It provides a single
primitive:
- * [pam\_chauthtok(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_chauthtok+3+NetBSD-5.0.1+i386)
- changes the authentication token, optionally verifying that it is
+ * [pam\_chauthtok(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_chauthtok+3+NetBSD-5.0.1+i386)
+ changes the authentication token, optionally verifying that it is
sufficiently hard to guess, has not been used previously, etc.
### Modules
-Modules are a very central concept in PAM; after all, they are the *M* in *PAM*.
-A PAM module is a self-contained piece of program code that implements the
-primitives in one or more facilities for one particular mechanism; possible
-mechanisms for the authentication facility, for instance, include the UNIX®
+Modules are a very central concept in PAM; after all, they are the *M* in *PAM*.
+A PAM module is a self-contained piece of program code that implements the
+primitives in one or more facilities for one particular mechanism; possible
+mechanisms for the authentication facility, for instance, include the UNIX®
password database, NIS, LDAP and Radius.
#### Module Naming
-FreeBSD and NetBSD implement each mechanism in a single module, named
-`pam_mechanism`.so (for instance, `pam_unix.so` for the UNIX mechanism.) Other
-implementations sometimes have separate modules for separate facilities, and
-include the facility name as well as the mechanism name in the module name. To
-name one example, Solaris has a `pam_dial_auth.so.1` module which is commonly
-used to authenticate dialup users. Also, almost every module has a man page with
-the same name, i.e.:
-[pam\_unix(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_unix+8+NetBSD-5.0.1+i386)
+FreeBSD and NetBSD implement each mechanism in a single module, named
+`pam_mechanism`.so (for instance, `pam_unix.so` for the UNIX mechanism.) Other
+implementations sometimes have separate modules for separate facilities, and
+include the facility name as well as the mechanism name in the module name. To
+name one example, Solaris has a `pam_dial_auth.so.1` module which is commonly
+used to authenticate dialup users. Also, almost every module has a man page with
+the same name, i.e.:
+[pam\_unix(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_unix+8+NetBSD-5.0.1+i386)
explains how the `pam_unix.so` module works.
#### Module Versioning
-FreeBSD's original PAM implementation, based on Linux-PAM, did not use version
-numbers for PAM modules. This would commonly cause problems with legacy
-applications, which might be linked against older versions of the system
-libraries, as there was no way to load a matching version of the required
+FreeBSD's original PAM implementation, based on Linux-PAM, did not use version
+numbers for PAM modules. This would commonly cause problems with legacy
+applications, which might be linked against older versions of the system
+libraries, as there was no way to load a matching version of the required
modules.
-OpenPAM, on the other hand, looks for modules that have the same version number
-as the PAM library (currently 2 in FreeBSD and 0 in NetBSD), and only falls back
-to an unversioned module if no versioned module could be loaded. Thus legacy
-modules can be provided for legacy applications, while allowing new (or newly
+OpenPAM, on the other hand, looks for modules that have the same version number
+as the PAM library (currently 2 in FreeBSD and 0 in NetBSD), and only falls back
+to an unversioned module if no versioned module could be loaded. Thus legacy
+modules can be provided for legacy applications, while allowing new (or newly
built) applications to take advantage of the most recent modules.
-Although Solaris PAM modules commonly have a version number, they're not truly
-versioned, because the number is a part of the module name and must be included
+Although Solaris PAM modules commonly have a version number, they're not truly
+versioned, because the number is a part of the module name and must be included
in the configuration.
#### Module Path
-There isn't a common directory for storing PAM modules. Under FreeBSD, they are
-located at `/usr/lib` and, under NetBSD, you can find them in
+There isn't a common directory for storing PAM modules. Under FreeBSD, they are
+located at `/usr/lib` and, under NetBSD, you can find them in
`/usr/lib/security`.
### Chains and policies
-When a server initiates a PAM transaction, the PAM library tries to load a
-policy for the service specified in the
-[pam\_start(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_start+3+NetBSD-5.0.1+i386)
-call. The policy specifies how authentication requests should be processed, and
-is defined in a configuration file. This is the other central concept in PAM:
-the possibility for the admin to tune the system security policy (in the wider
+When a server initiates a PAM transaction, the PAM library tries to load a
+policy for the service specified in the
+[pam\_start(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_start+3+NetBSD-5.0.1+i386)
+call. The policy specifies how authentication requests should be processed, and
+is defined in a configuration file. This is the other central concept in PAM:
+the possibility for the admin to tune the system security policy (in the wider
sense of the word) simply by editing a text file.
-A policy consists of four chains, one for each of the four PAM facilities. Each
-chain is a sequence of configuration statements, each specifying a module to
-invoke, some (optional) parameters to pass to the module, and a control flag
+A policy consists of four chains, one for each of the four PAM facilities. Each
+chain is a sequence of configuration statements, each specifying a module to
+invoke, some (optional) parameters to pass to the module, and a control flag
that describes how to interpret the return code from the module.
-Understanding the control flags is essential to understanding PAM configuration
+Understanding the control flags is essential to understanding PAM configuration
files. There are a number of different control flags:
- * `binding` -- If the module succeeds and no earlier module in the chain has
- failed, the chain is immediately terminated and the request is granted. If
- the module fails, the rest of the chain is executed, but the request is
+ * `binding` -- If the module succeeds and no earlier module in the chain has
+ failed, the chain is immediately terminated and the request is granted. If
+ the module fails, the rest of the chain is executed, but the request is
ultimately denied.
- This control flag was introduced by Sun in Solaris 9 (SunOS 5.9), and is also supported by OpenPAM.
+ This control flag was introduced by Sun in Solaris 9 (SunOS 5.9), and is also
+ supported by OpenPAM.
- * `required` -- If the module succeeds, the rest of the chain is executed, and
- the request is granted unless some other module fails. If the module fails,
+ * `required` -- If the module succeeds, the rest of the chain is executed, and
+ the request is granted unless some other module fails. If the module fails,
the rest of the chain is also executed, but the request is ultimately denied.
- * `requisite` -- If the module succeeds, the rest of the chain is executed, and
- the request is granted unless some other module fails. If the module fails,
+ * `requisite` -- If the module succeeds, the rest of the chain is executed, and
+ the request is granted unless some other module fails. If the module fails,
the chain is immediately terminated and the request is denied.
- * `sufficient` -- If the module succeeds and no earlier module in the chain has
- failed, the chain is immediately terminated and the request is granted. If
- the module fails, the module is ignored and the rest of the chain is
+ * `sufficient` -- If the module succeeds and no earlier module in the chain has
+ failed, the chain is immediately terminated and the request is granted. If
+ the module fails, the module is ignored and the rest of the chain is
executed.
- As the semantics of this flag may be somewhat confusing, especially when it is used for the last module in a chain, it is recommended that the `binding` control flag be used instead if the implementation supports it.
+ As the semantics of this flag may be somewhat confusing, especially when it
+ is used for the last module in a chain, it is recommended that the `binding`
+ control flag be used instead if the implementation supports it.
- * `optional` -- The module is executed, but its result is ignored. If all
- modules in a chain are marked `optional`, all requests will always be
+ * `optional` -- The module is executed, but its result is ignored. If all
+ modules in a chain are marked `optional`, all requests will always be
granted.
-When a server invokes one of the six PAM primitives, PAM retrieves the chain for
-the facility the primitive belongs to, and invokes each of the modules listed in
-the chain, in the order they are listed, until it reaches the end, or determines
-that no further processing is necessary (either because a `binding` or
-`sufficient` module succeeded, or because a `requisite` module failed.) The
-request is granted if and only if at least one module was invoked, and all
+When a server invokes one of the six PAM primitives, PAM retrieves the chain for
+the facility the primitive belongs to, and invokes each of the modules listed in
+the chain, in the order they are listed, until it reaches the end, or determines
+that no further processing is necessary (either because a `binding` or
+`sufficient` module succeeded, or because a `requisite` module failed.) The
+request is granted if and only if at least one module was invoked, and all
non-optional modules succeeded.
-Note that it is possible, though not very common, to have the same module listed
-several times in the same chain. For instance, a module that looks up user names
-and passwords in a directory server could be invoked multiple times with
-different parameters specifying different directory servers to contact. PAM
-treat different occurrences of the same module in the same chain as different,
+Note that it is possible, though not very common, to have the same module listed
+several times in the same chain. For instance, a module that looks up user names
+and passwords in a directory server could be invoked multiple times with
+different parameters specifying different directory servers to contact. PAM
+treat different occurrences of the same module in the same chain as different,
unrelated modules.
### Transactions
-The lifecycle of a typical PAM transaction is described below. Note that if any
-of these steps fails, the server should report a suitable error message to the
+The lifecycle of a typical PAM transaction is described below. Note that if any
+of these steps fails, the server should report a suitable error message to the
client and abort the transaction.
- 1. If necessary, the server obtains arbitrator credentials through a mechanism
- independent of PAM -- most commonly by virtue of having been started by `root`,
+ 1. If necessary, the server obtains arbitrator credentials through a mechanism
+ independent of PAM -- most commonly by virtue of having been started by `root`,
or of being setuid `root`.
- 2. The server calls
- [pam\_start(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_start+3+NetBSD-5.0.1+i386)
- to initialize the PAM library and specify its service name and the target
+ 2. The server calls
+ [pam\_start(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_start+3+NetBSD-5.0.1+i386)
+ to initialize the PAM library and specify its service name and the target
account, and register a suitable conversation function.
- 3. The server obtains various information relating to the transaction (such as
- the applicant's user name and the name of the host the client runs on) and
- submits it to PAM using
+ 3. The server obtains various information relating to the transaction (such as
+ the applicant's user name and the name of the host the client runs on) and
+ submits it to PAM using
[pam\_set\_item(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_set_item+3+NetBSD-5.0.1+i386).
- 4. The server calls
- [pam\_authenticate(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_authenticate+3+NetBSD-5.0.1+i386)
+ 4. The server calls
+ [pam\_authenticate(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_authenticate+3+NetBSD-5.0.1+i386)
to authenticate the applicant.
- 5. The server calls
- [pam\_acct\_mgmt(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_acct_mgmt+3+NetBSD-5.0.1+i386)
- to verify that the requested account is available and valid. If the password is
- correct but has expired,
- [pam\_acct\_mgmt(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_acct_mgmt+3+NetBSD-5.0.1+i386)
+ 5. The server calls
+ [pam\_acct\_mgmt(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_acct_mgmt+3+NetBSD-5.0.1+i386)
+ to verify that the requested account is available and valid. If the password is
+ correct but has expired,
+ [pam\_acct\_mgmt(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_acct_mgmt+3+NetBSD-5.0.1+i386)
will return `PAM_NEW_AUTHTOK_REQD` instead of `PAM_SUCCESS`.
- 6. If the previous step returned `PAM_NEW_AUTHTOK_REQD`, the server now calls
- [pam\_chauthtok(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_chauthtok+3+NetBSD-5.0.1+i386)
- to force the client to change the authentication token for the requested
+ 6. If the previous step returned `PAM_NEW_AUTHTOK_REQD`, the server now calls
+ [pam\_chauthtok(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_chauthtok+3+NetBSD-5.0.1+i386)
+ to force the client to change the authentication token for the requested
account.
- 7. Now that the applicant has been properly authenticated, the server calls
- [pam\_setcred(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_setcred+3+NetBSD-5.0.1+i386)
- to establish the credentials of the requested account. It is able to do this
- because it acts on behalf of the arbitrator, and holds the arbitrator's
+ 7. Now that the applicant has been properly authenticated, the server calls
+ [pam\_setcred(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_setcred+3+NetBSD-5.0.1+i386)
+ to establish the credentials of the requested account. It is able to do this
+ because it acts on behalf of the arbitrator, and holds the arbitrator's
credentials.
- 8. Once the correct credentials have been established, the server calls
- [pam\_open\_session(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_open_session+3+NetBSD-5.0.1+i386)
+ 8. Once the correct credentials have been established, the server calls
+ [pam\_open\_session(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_open_session+3+NetBSD-5.0.1+i386)
to set up the session.
- 9. The server now performs whatever service the client requested -- for
+ 9. The server now performs whatever service the client requested -- for
instance, provide the applicant with a shell.
-10. Once the server is done serving the client, it calls
- [pam\_close\_session(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_close_session+3+NetBSD-5.0.1+i386)
+10. Once the server is done serving the client, it calls
+ [pam\_close\_session(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_close_session+3+NetBSD-5.0.1+i386)
to tear down the session.
-11. Finally, the server calls
- [pam\_end(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_end+3+NetBSD-5.0.1+i386)
- to notify the PAM library that it is done and that it can release whatever
+11. Finally, the server calls
+ [pam\_end(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_end+3+NetBSD-5.0.1+i386)
+ to notify the PAM library that it is done and that it can release whatever
resources it has allocated in the course of the transaction.
## PAM Configuration
@@ -387,108 +400,108 @@ client and abort the transaction.
#### The `/etc/pam.conf` file
-The traditional PAM policy file is `/etc/pam.conf`. This file contains all the
-PAM policies for your system. Each line of the file describes one step in a
+The traditional PAM policy file is `/etc/pam.conf`. This file contains all the
+PAM policies for your system. Each line of the file describes one step in a
chain, as shown below:
login auth required pam_nologin.so no_warn
-The fields are, in order: service name, facility name, control flag, module
-name, and module arguments. Any additional fields are interpreted as additional
+The fields are, in order: service name, facility name, control flag, module
+name, and module arguments. Any additional fields are interpreted as additional
module arguments.
-A separate chain is constructed for each service / facility pair, so while the
-order in which lines for the same service and facility appear is significant,
-the order in which the individual services and facilities are listed is not. The
-examples in the original PAM paper grouped configuration lines by facility, and
-the Solaris stock `pam.conf` still does that, but FreeBSD's stock configuration
-groups configuration lines by service. Either way is fine; either way makes
+A separate chain is constructed for each service / facility pair, so while the
+order in which lines for the same service and facility appear is significant,
+the order in which the individual services and facilities are listed is not. The
+examples in the original PAM paper grouped configuration lines by facility, and
+the Solaris stock `pam.conf` still does that, but FreeBSD's stock configuration
+groups configuration lines by service. Either way is fine; either way makes
equal sense.
#### The `/etc/pam.d` directory
-OpenPAM and Linux-PAM support an alternate configuration mechanism, which is the
-preferred mechanism in FreeBSD and NetBSD. In this scheme, each policy is
-contained in a separate file bearing the name of the service it applies to.
+OpenPAM and Linux-PAM support an alternate configuration mechanism, which is the
+preferred mechanism in FreeBSD and NetBSD. In this scheme, each policy is
+contained in a separate file bearing the name of the service it applies to.
These files are stored in `/etc/pam.d/`.
-These per-service policy files have only four fields instead of `pam.conf`'s
-five: the service name field is omitted. Thus, instead of the sample `pam.conf`
-line from the previous section, one would have the following line in
+These per-service policy files have only four fields instead of `pam.conf`'s
+five: the service name field is omitted. Thus, instead of the sample `pam.conf`
+line from the previous section, one would have the following line in
`/etc/pam.d/login`:
auth required pam_nologin.so no_warn
-As a consequence of this simplified syntax, it is possible to use the same
-policy for multiple services by linking each service name to a same policy file.
-For instance, to use the same policy for the `su` and `sudo` services, one could
+As a consequence of this simplified syntax, it is possible to use the same
+policy for multiple services by linking each service name to a same policy file.
+For instance, to use the same policy for the `su` and `sudo` services, one could
do as follows:
# cd /etc/pam.d
# ln -s su sudo
-This works because the service name is determined from the file name rather than
-specified in the policy file, so the same file can be used for multiple
+This works because the service name is determined from the file name rather than
+specified in the policy file, so the same file can be used for multiple
differently-named services.
-Since each service's policy is stored in a separate file, the `pam.d` mechanism
-also makes it very easy to install additional policies for third-party software
+Since each service's policy is stored in a separate file, the `pam.d` mechanism
+also makes it very easy to install additional policies for third-party software
packages.
#### The policy search order
-As we have seen above, PAM policies can be found in a number of places. If no
-configuration file is found for a particular service, the `/etc/pam.d/other` is
-used instead. If that file does not exist, `/etc/pam.conf` is searched for
+As we have seen above, PAM policies can be found in a number of places. If no
+configuration file is found for a particular service, the `/etc/pam.d/other` is
+used instead. If that file does not exist, `/etc/pam.conf` is searched for
entries matching he specified service or, failing that, the "other" service.
-It is essential to understand that PAM's configuration system is centered on
+It is essential to understand that PAM's configuration system is centered on
chains.
### Breakdown of a configuration line
-As explained in the [PAM policy files](chap-pam.html#pam-config-file "18.5.1.
-PAM policy files") section, each line in `/etc/pam.conf` consists of four or
-more fields: the service name, the facility name, the control flag, the module
+As explained in the [PAM policy files](chap-pam.html#pam-config-file "18.5.1.
+PAM policy files") section, each line in `/etc/pam.conf` consists of four or
+more fields: the service name, the facility name, the control flag, the module
name, and zero or more module arguments.
-The service name is generally (though not always) the name of the application
-the statement applies to. If you are unsure, refer to the individual
+The service name is generally (though not always) the name of the application
+the statement applies to. If you are unsure, refer to the individual
application's documentation to determine what service name it uses.
-Note that if you use `/etc/pam.d/` instead of `/etc/pam.conf`, the service name
-is specified by the name of the policy file, and omitted from the actual
+Note that if you use `/etc/pam.d/` instead of `/etc/pam.conf`, the service name
+is specified by the name of the policy file, and omitted from the actual
configuration lines, which then start with the facility name.
The facility is one of the four facility keywords described in the
[[Facilities and primitives|guide/pam#facilities-primitives]]] section.
-Likewise, the control flag is one of the four keywords described in the [[Chains
-and policies|guide/pam#chains-policies]] section, describing how to interpret
-the return code from the module. Linux-PAM supports an alternate syntax that
-lets you specify the action to associate with each possible return code, but
-this should be avoided as it is non-standard and closely tied in with the way
-Linux-PAM dispatches service calls (which differs greatly from the way Solaris
+Likewise, the control flag is one of the four keywords described in the [[Chains
+and policies|guide/pam#chains-policies]] section, describing how to interpret
+the return code from the module. Linux-PAM supports an alternate syntax that
+lets you specify the action to associate with each possible return code, but
+this should be avoided as it is non-standard and closely tied in with the way
+Linux-PAM dispatches service calls (which differs greatly from the way Solaris
and OpenPAM do it.) Unsurprisingly, OpenPAM does not support this syntax.
### Policies
-To configure PAM correctly, it is essential to understand how policies are
+To configure PAM correctly, it is essential to understand how policies are
interpreted.
-When an application calls
-[pam\_start(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_start+3+NetBSD-5.0.1+i386),
-the PAM library loads the policy for the specified service and constructs four
-module chains (one for each facility.) If one or more of these chains are empty,
-the corresponding chains from the policy for the `other` service are
+When an application calls
+[pam\_start(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_start+3+NetBSD-5.0.1+i386),
+the PAM library loads the policy for the specified service and constructs four
+module chains (one for each facility.) If one or more of these chains are empty,
+the corresponding chains from the policy for the `other` service are
substituted.
-When the application later calls one of the six PAM primitives, the PAM library
-retrieves the chain for the corresponding facility and calls the appropriate
-service function in each module listed in the chain, in the order in which they
-were listed in the configuration. After each call to a service function, the
-module type and the error code returned by the service function are used to
-determine what happens next. With a few exceptions, which we discuss below, the
+When the application later calls one of the six PAM primitives, the PAM library
+retrieves the chain for the corresponding facility and calls the appropriate
+service function in each module listed in the chain, in the order in which they
+were listed in the configuration. After each call to a service function, the
+module type and the error code returned by the service function are used to
+determine what happens next. With a few exceptions, which we discuss below, the
following table applies:
[[!table data="""
@@ -500,23 +513,23 @@ sufficient | if (!fail) break; | -
optional | - | - | -
"""]]
-If `fail` is true at the end of a chain, or when a `break` is reached, the
-dispatcher returns the error code returned by the first module that failed.
+If `fail` is true at the end of a chain, or when a `break` is reached, the
+dispatcher returns the error code returned by the first module that failed.
Otherwise, it returns `PAM_SUCCESS`.
-The first exception of note is that the error code `PAM_NEW_AUTHTOK_REQD` is
-treated like a success, except that if no module failed, and at least one module
-returned `PAM_NEW_AUTHTOK_REQD`, the dispatcher will return
+The first exception of note is that the error code `PAM_NEW_AUTHTOK_REQD` is
+treated like a success, except that if no module failed, and at least one module
+returned `PAM_NEW_AUTHTOK_REQD`, the dispatcher will return
`PAM_NEW_AUTHTOK_REQD`.
-The second exception is that
-[pam\_setcred(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_setcred+3+NetBSD-5.0.1+i386)
+The second exception is that
+[pam\_setcred(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_setcred+3+NetBSD-5.0.1+i386)
treats `binding` and `sufficient` modules as if they were `required`.
-The third and final exception is that
-[pam\_chauthtok(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_chauthtok+3+NetBSD-5.0.1+i386)
-runs the entire chain twice (once for preliminary checks and once to actually
-set the password), and in the preliminary phase it treats `binding` and
+The third and final exception is that
+[pam\_chauthtok(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_chauthtok+3+NetBSD-5.0.1+i386)
+runs the entire chain twice (once for preliminary checks and once to actually
+set the password), and in the preliminary phase it treats `binding` and
`sufficient` modules as if they were `required`.
## PAM modules
@@ -525,214 +538,214 @@ set the password), and in the preliminar
#### pam\_deny(8)
-The
-[pam\_deny(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_deny+8+NetBSD-5.0.1+i386)
-module is one of the simplest modules available; it responds to any request with
-`PAM_AUTH_ERR`. It is useful for quickly disabling a service (add it to the top
+The
+[pam\_deny(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_deny+8+NetBSD-5.0.1+i386)
+module is one of the simplest modules available; it responds to any request with
+`PAM_AUTH_ERR`. It is useful for quickly disabling a service (add it to the top
of every chain), or for terminating chains of `sufficient` modules.
#### pam\_echo(8)
-The
-[pam\_echo(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_echo+8+NetBSD-5.0.1+i386)
-module simply passes its arguments to the conversation function as a
-`PAM_TEXT_INFO` message. It is mostly useful for debugging, but can also serve
-to display messages such as `Unauthorized access will be prosecuted` before
+The
+[pam\_echo(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_echo+8+NetBSD-5.0.1+i386)
+module simply passes its arguments to the conversation function as a
+`PAM_TEXT_INFO` message. It is mostly useful for debugging, but can also serve
+to display messages such as `Unauthorized access will be prosecuted` before
starting the authentication procedure.
#### pam\_exec(8)
-The
-[pam\_exec(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_exec+8+NetBSD-5.0.1+i386)
-module takes its first argument to be the name of a program to execute, and the
-remaining arguments are passed to that program as command-line arguments. One
-possible application is to use it to run a program at login time which mounts
+The
+[pam\_exec(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_exec+8+NetBSD-5.0.1+i386)
+module takes its first argument to be the name of a program to execute, and the
+remaining arguments are passed to that program as command-line arguments. One
+possible application is to use it to run a program at login time which mounts
the user's home directory.
#### pam\_ftpusers(8)
-The
-[pam\_ftpusers(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_ftpusers+8+NetBSD-5.0.1+i386)
-module successes if and only if the user is listed in `/etc/ftpusers`.
-Currently, in NetBSD, this module doesn't understand the extended syntax of
-[ftpd(8)](http://netbsd.gw.com/cgi-bin/man-cgi?ftpd+8+NetBSD-5.0.1+i386), but
+The
+[pam\_ftpusers(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_ftpusers+8+NetBSD-5.0.1+i386)
+module successes if and only if the user is listed in `/etc/ftpusers`.
+Currently, in NetBSD, this module doesn't understand the extended syntax of
+[ftpd(8)](http://netbsd.gw.com/cgi-bin/man-cgi?ftpd+8+NetBSD-5.0.1+i386), but
this will be fixed in the future.
#### pam\_group(8)
-The
-[pam\_group(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_group+8+NetBSD-5.0.1+i386)
-module accepts or rejects applicants on the basis of their membership in a
-particular file group (normally `wheel` for
-[su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386)). It is
-primarily intended for maintaining the traditional behaviour of BSD
-[su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386), but has
-many other uses, such as excluding certain groups of users from a particular
+The
+[pam\_group(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_group+8+NetBSD-5.0.1+i386)
+module accepts or rejects applicants on the basis of their membership in a
+particular file group (normally `wheel` for
+[su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386)). It is
+primarily intended for maintaining the traditional behaviour of BSD
+[su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386), but has
+many other uses, such as excluding certain groups of users from a particular
service.
-In NetBSD, there is an argument called `authenticate` in which the user is asked
+In NetBSD, there is an argument called `authenticate` in which the user is asked
to authenticate using his own password.
#### pam\_guest(8)
-The
-[pam\_guest(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_guest+8+NetBSD-5.0.1+i386)
-module allows guest logins using fixed login names. Various requirements can be
-placed on the password, but the default behaviour is to allow any password as
-long as the login name is that of a guest account. The
-[pam\_guest(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_guest+8+NetBSD-5.0.1+i386)
+The
+[pam\_guest(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_guest+8+NetBSD-5.0.1+i386)
+module allows guest logins using fixed login names. Various requirements can be
+placed on the password, but the default behaviour is to allow any password as
+long as the login name is that of a guest account. The
+[pam\_guest(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_guest+8+NetBSD-5.0.1+i386)
module can easily be used to implement anonymous FTP logins.
#### pam\_krb5(8)
-The
-[pam\_krb5(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_krb5+8+NetBSD-5.0.1+i386)
-module provides functions to verify the identity of a user and to set user
-specific credentials using Kerberos 5. It prompts the user for a password and
-obtains a new Kerberos TGT for the principal. The TGT is verified by obtaining a
-service ticket for the local host. The newly acquired credentials are stored in
-a credential cache and the environment variable KRB5CCNAME is set appropriately.
-The credentials cache should be destroyed by the user at logout with
+The
+[pam\_krb5(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_krb5+8+NetBSD-5.0.1+i386)
+module provides functions to verify the identity of a user and to set user
+specific credentials using Kerberos 5. It prompts the user for a password and
+obtains a new Kerberos TGT for the principal. The TGT is verified by obtaining a
+service ticket for the local host. The newly acquired credentials are stored in
+a credential cache and the environment variable KRB5CCNAME is set appropriately.
+The credentials cache should be destroyed by the user at logout with
[kdestroy(1)](http://netbsd.gw.com/cgi-bin/man-cgi?kdestroy+1+NetBSD-5.0.1+i386).
#### pam\_ksu(8)
-The
-[pam\_ksu(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_ksu+8+NetBSD-5.0.1+i386)
-module provides only authentication services for Kerberos 5 to determine whether
-or not the applicant is authorized to obtain the privileges of the target
+The
+[pam\_ksu(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_ksu+8+NetBSD-5.0.1+i386)
+module provides only authentication services for Kerberos 5 to determine whether
+or not the applicant is authorized to obtain the privileges of the target
account.
#### pam\_lastlog(8)
-The
-[pam\_lastlog(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_lastlog+8+NetBSD-5.0.1+i386)
-module provides only session management services. It records the session in
-[utmp(5)](http://netbsd.gw.com/cgi-bin/man-cgi?utmp+5+NetBSD-5.0.1+i386),
-[utmpx(5)](http://netbsd.gw.com/cgi-bin/man-cgi?utmpx+5+NetBSD-5.0.1+i386),
-[wtmp(5)](http://netbsd.gw.com/cgi-bin/man-cgi?wtmp+5+NetBSD-5.0.1+i386),
-[wtmpx(5)](http://netbsd.gw.com/cgi-bin/man-cgi?wtmpx+5+NetBSD-5.0.1+i386),
-[lastlog(5)](http://netbsd.gw.com/cgi-bin/man-cgi?lastlog+5+NetBSD-5.0.1+i386)
-and
-[lastlogx(5)](http://netbsd.gw.com/cgi-bin/man-cgi?lastlogx+5+NetBSD-5.0.1+i386)
+The
+[pam\_lastlog(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_lastlog+8+NetBSD-5.0.1+i386)
+module provides only session management services. It records the session in
+[utmp(5)](http://netbsd.gw.com/cgi-bin/man-cgi?utmp+5+NetBSD-5.0.1+i386),
+[utmpx(5)](http://netbsd.gw.com/cgi-bin/man-cgi?utmpx+5+NetBSD-5.0.1+i386),
+[wtmp(5)](http://netbsd.gw.com/cgi-bin/man-cgi?wtmp+5+NetBSD-5.0.1+i386),
+[wtmpx(5)](http://netbsd.gw.com/cgi-bin/man-cgi?wtmpx+5+NetBSD-5.0.1+i386),
+[lastlog(5)](http://netbsd.gw.com/cgi-bin/man-cgi?lastlog+5+NetBSD-5.0.1+i386)
+and
+[lastlogx(5)](http://netbsd.gw.com/cgi-bin/man-cgi?lastlogx+5+NetBSD-5.0.1+i386)
databases.
#### pam\_login\_access(8)
-The
-[pam\_login\_access(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_login_access+8+NetBSD-5.0.1+i386)
-module provides an implementation of the account management primitive which
-enforces the login restrictions specified in the
-[login.access(5)](http://netbsd.gw.com/cgi-bin/man-cgi?login.access+5+NetBSD-5.0.1+i386)
+The
+[pam\_login\_access(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_login_access+8+NetBSD-5.0.1+i386)
+module provides an implementation of the account management primitive which
+enforces the login restrictions specified in the
+[login.access(5)](http://netbsd.gw.com/cgi-bin/man-cgi?login.access+5+NetBSD-5.0.1+i386)
table.
#### pam\_nologin(8)
-The
-[pam\_nologin(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_nologin+8+NetBSD-5.0.1+i386)
-module refuses non-root logins when `/var/run/nologin` exists. This file is
-normally created by
-[shutdown(8)](http://netbsd.gw.com/cgi-bin/man-cgi?shutdown+8+NetBSD-5.0.1+i386)
+The
+[pam\_nologin(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_nologin+8+NetBSD-5.0.1+i386)
+module refuses non-root logins when `/var/run/nologin` exists. This file is
+normally created by
+[shutdown(8)](http://netbsd.gw.com/cgi-bin/man-cgi?shutdown+8+NetBSD-5.0.1+i386)
when less than five minutes remain until the scheduled shutdown time.
#### pam\_permit(8)
-The
-[pam\_permit(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_permit+8+NetBSD-5.0.1+i386)
-module is one of the simplest modules available; it responds to any request with
-`PAM_SUCCESS`. It is useful as a placeholder for services where one or more
+The
+[pam\_permit(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_permit+8+NetBSD-5.0.1+i386)
+module is one of the simplest modules available; it responds to any request with
+`PAM_SUCCESS`. It is useful as a placeholder for services where one or more
chains would otherwise be empty.
#### pam\_radius(8)
-The
-[pam\_radius(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_radius+8+NetBSD-5.0.1+i386)
-module provides authentication services based upon the RADIUS (Remote
+The
+[pam\_radius(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_radius+8+NetBSD-5.0.1+i386)
+module provides authentication services based upon the RADIUS (Remote
Authentication Dial In User Service) protocol.
#### pam\_rhosts(8)
-The
-[pam\_rhosts(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_rhosts+8+NetBSD-5.0.1+i386)
-module provides only authentication services. It reports success if and only if
-the target user's ID is not 0 and the remote host and user are listed in
+The
+[pam\_rhosts(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_rhosts+8+NetBSD-5.0.1+i386)
+module provides only authentication services. It reports success if and only if
+the target user's ID is not 0 and the remote host and user are listed in
`/etc/hosts.equiv` or in the target user's `~/.rhosts`.
#### pam\_rootok(8)
-The
-[pam\_rootok(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_rootok+8+NetBSD-5.0.1+i386)
-module reports success if and only if the real user id of the process calling it
-(which is assumed to be run by the applicant) is 0. This is useful for
-non-networked services such as
-[su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386) or
-[passwd(1)](http://netbsd.gw.com/cgi-bin/man-cgi?passwd+1+NetBSD-5.0.1+i386), to
+The
+[pam\_rootok(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_rootok+8+NetBSD-5.0.1+i386)
+module reports success if and only if the real user id of the process calling it
+(which is assumed to be run by the applicant) is 0. This is useful for
+non-networked services such as
+[su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386) or
+[passwd(1)](http://netbsd.gw.com/cgi-bin/man-cgi?passwd+1+NetBSD-5.0.1+i386), to
which the `root` should have automatic access.
#### pam\_securetty(8)
-The
-[pam\_securetty(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_securetty+8+NetBSD-5.0.1+i386)
-module provides only account services. It is used when the applicant is
-attempting to authenticate as superuser, and the process is attached to an
+The
+[pam\_securetty(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_securetty+8+NetBSD-5.0.1+i386)
+module provides only account services. It is used when the applicant is
+attempting to authenticate as superuser, and the process is attached to an
insecure TTY.
#### pam\_self(8)
-The
-[pam\_self(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_self+8+NetBSD-5.0.1+i386)
-module reports success if and only if the names of the applicant matches that of
-the target account. It is most useful for non-networked services such as
-[su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386), where the
+The
+[pam\_self(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_self+8+NetBSD-5.0.1+i386)
+module reports success if and only if the names of the applicant matches that of
+the target account. It is most useful for non-networked services such as
+[su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386), where the
identity of the applicant can be easily verified.
#### pam\_ssh(8)
-The
-[pam\_ssh(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_ssh+8+NetBSD-5.0.1+i386)
-module provides both authentication and session services. The authentication
-service allows users who have passphrase-protected SSH secret keys in their
-`~/.ssh` directory to authenticate themselves by typing their passphrase. The
-session service starts
-[ssh-agent(1)](http://netbsd.gw.com/cgi-bin/man-cgi?ssh-agent+1+NetBSD-5.0.1+i386)
-and preloads it with the keys that were decrypted in the authentication phase.
-This feature is particularly useful for local logins, whether in X (using
-[xdm(1)](http://netbsd.gw.com/cgi-bin/man-cgi?xdm+1+NetBSD-5.0.1+i386) or
+The
+[pam\_ssh(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_ssh+8+NetBSD-5.0.1+i386)
+module provides both authentication and session services. The authentication
+service allows users who have passphrase-protected SSH secret keys in their
+`~/.ssh` directory to authenticate themselves by typing their passphrase. The
+session service starts
+[ssh-agent(1)](http://netbsd.gw.com/cgi-bin/man-cgi?ssh-agent+1+NetBSD-5.0.1+i386)
+and preloads it with the keys that were decrypted in the authentication phase.
+This feature is particularly useful for local logins, whether in X (using
+[xdm(1)](http://netbsd.gw.com/cgi-bin/man-cgi?xdm+1+NetBSD-5.0.1+i386) or
another PAM-aware X login manager) or at the console.
-This module implements what is fundamentally a password authentication scheme.
-Care should be taken to only use this module over a secure session (secure TTY,
-encrypted session, etc.), otherwise the user's SSH passphrase could be
+This module implements what is fundamentally a password authentication scheme.
+Care should be taken to only use this module over a secure session (secure TTY,
+encrypted session, etc.), otherwise the user's SSH passphrase could be
compromised.
-Additional consideration should be given to the use of
-[pam\_ssh(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_ssh+8+NetBSD-5.0.1+i386).
-Users often assume that file permissions are sufficient to protect their SSH
-keys, and thus use weak or no passphrases. Since the system administrator has no
-effective means of enforcing SSH passphrase quality, this has the potential to
+Additional consideration should be given to the use of
+[pam\_ssh(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_ssh+8+NetBSD-5.0.1+i386).
+Users often assume that file permissions are sufficient to protect their SSH
+keys, and thus use weak or no passphrases. Since the system administrator has no
+effective means of enforcing SSH passphrase quality, this has the potential to
expose the system to security risks.
#### pam\_unix(8)
-The
-[pam\_unix(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_unix+8+NetBSD-5.0.1+i386)
-module implements traditional UNIX® password authentication, using
-[getpwnam(3)](http://netbsd.gw.com/cgi-bin/man-cgi?getpwnam+3+NetBSD-5.0.1+i386)
-under FreeBSD or
-[getpwnam\_r(3)](http://netbsd.gw.com/cgi-bin/man-cgi?getpwnam_r+3+NetBSD-5.0.1+i386)
-under NetBSD to obtain the target account's password and compare it with the one
-provided by the applicant. It also provides account management services
-(enforcing account and password expiration times) and password-changing
-services. This is probably the single most useful module, as the great majority
+The
+[pam\_unix(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_unix+8+NetBSD-5.0.1+i386)
+module implements traditional UNIX® password authentication, using
+[getpwnam(3)](http://netbsd.gw.com/cgi-bin/man-cgi?getpwnam+3+NetBSD-5.0.1+i386)
+under FreeBSD or
+[getpwnam\_r(3)](http://netbsd.gw.com/cgi-bin/man-cgi?getpwnam_r+3+NetBSD-5.0.1+i386)
+under NetBSD to obtain the target account's password and compare it with the one
+provided by the applicant. It also provides account management services
+(enforcing account and password expiration times) and password-changing
+services. This is probably the single most useful module, as the great majority
of admins will want to maintain historical behaviour for at least some services.
### NetBSD-specific PAM Modules
#### pam\_skey(8)
-The
-[pam\_skey(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_skey+8+NetBSD-5.0.1+i386)
-module implements S/Key One Time Password (OTP) authentication methods, using
+The
+[pam\_skey(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_skey+8+NetBSD-5.0.1+i386)
+module implements S/Key One Time Password (OTP) authentication methods, using
the `/etc/skeykeys` database.
## PAM Application Programming
@@ -745,16 +758,16 @@ This section has not yet been written.
## Sample PAM Application
-The following is a minimal implementation of
-[su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386) using PAM.
-Note that it uses the OpenPAM-specific
-[openpam\_ttyconv(3)](http://netbsd.gw.com/cgi-bin/man-cgi?openpam_ttyconv+3+NetBSD-5.0.1+i386)
-conversation function, which is prototyped in `security/openpam.h`. If you wish
-build this application on a system with a different PAM library, you will have
-to provide your own conversation function. A robust conversation function is
-surprisingly difficult to implement; the one presented in the [Sample PAM
-Conversation Function](chap-pam.html#pam-sample-conv "18.11. Sample PAM
-Conversation Function") sub-chapter is a good starting point, but should not be
+The following is a minimal implementation of
+[su(1)](http://netbsd.gw.com/cgi-bin/man-cgi?su+1+NetBSD-5.0.1+i386) using PAM.
+Note that it uses the OpenPAM-specific
+[openpam\_ttyconv(3)](http://netbsd.gw.com/cgi-bin/man-cgi?openpam_ttyconv+3+NetBSD-5.0.1+i386)
+conversation function, which is prototyped in `security/openpam.h`. If you wish
+build this application on a system with a different PAM library, you will have
+to provide your own conversation function. A robust conversation function is
+surprisingly difficult to implement; the one presented in the [Sample PAM
+Conversation Function](chap-pam.html#pam-sample-conv "18.11. Sample PAM
+Conversation Function") sub-chapter is a good starting point, but should not be
used in real-world applications.
#include
@@ -909,12 +922,12 @@ used in real-world applications.
## Sample PAM Module
-The following is a minimal implementation of
-[pam\_unix(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_unix+8+NetBSD-5.0.1+i386),
-offering only authentication services. It should build and run with most PAM
-implementations, but takes advantage of OpenPAM extensions if available: note
-the use of
-[pam\_get\_authtok(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_get_authtok+3+NetBSD-5.0.1+i386),
+The following is a minimal implementation of
+[pam\_unix(8)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_unix+8+NetBSD-5.0.1+i386),
+offering only authentication services. It should build and run with most PAM
+implementations, but takes advantage of OpenPAM extensions if available: note
+the use of
+[pam\_get\_authtok(3)](http://netbsd.gw.com/cgi-bin/man-cgi?pam_get_authtok+3+NetBSD-5.0.1+i386),
which enormously simplifies prompting the user for a password.
#include
@@ -1051,15 +1064,15 @@ which enormously simplifies prompting th
## Sample PAM Conversation Function
-The conversation function presented below is a greatly simplified version of
-OpenPAM's
-[openpam\_ttyconv(3)](http://netbsd.gw.com/cgi-bin/man-cgi?openpam_ttyconv+3+NetBSD-5.0.1+i386).
-It is fully functional, and should give the reader a good idea of how a
-conversation function should behave, but it is far too simple for real-world
-use. Even if you're not using OpenPAM, feel free to download the source code and
-adapt
-[openpam\_ttyconv(3)](http://netbsd.gw.com/cgi-bin/man-cgi?openpam_ttyconv+3+NetBSD-5.0.1+i386)
-to your uses; we believe it to be as robust as a tty-oriented conversation
+The conversation function presented below is a greatly simplified version of
+OpenPAM's
+[openpam\_ttyconv(3)](http://netbsd.gw.com/cgi-bin/man-cgi?openpam_ttyconv+3+NetBSD-5.0.1+i386).
+It is fully functional, and should give the reader a good idea of how a
+conversation function should behave, but it is far too simple for real-world
+use. Even if you're not using OpenPAM, feel free to download the source code and
+adapt
+[openpam\_ttyconv(3)](http://netbsd.gw.com/cgi-bin/man-cgi?openpam_ttyconv+3+NetBSD-5.0.1+i386)
+to your uses; we believe it to be as robust as a tty-oriented conversation
function can reasonably get.
#include